Method of heat-treating surface hardened articles



July 22, 1952 A. w. HERBENAR METHOD OF HEAT-TREATING SURFACE HARDENEDARTICLES Filed April 7, 1949 IN V EN TOR.

W44 fwc/r/vess 4/vra/v 1M 1905mm? Arman/5y w w as Patented July 22, 1952METHOD OF HEAT-TREATING SURFACE I HARDENED ARTICLES Anton W. Herbenar,Ferndale, Mich, assignor to The Ohio Crankshaft Company, Cleveland,Ohio, a corporation of Ohio Application April 7, 1949, Serial No. 86,078

This invention pertainsto the art 'of metal heating and, moreparticularly, to the heating of metals for the purposes of drawing ortempering hardened layers or surf aces thereon.

An object of the present invention is to provide a new and improvedmethod for drawing or tempering hardened layers or surfaces on metallicarticles of manufacture which permits of ready control of the amount ofdraw, which permits of a substantially uniform draw throughout theentire hardened layer and which avoids the objections of the prior art.

Another object of the invention is ;to provide a new and improved methodfor drawing a hardened surface or layer on a metallic article ofmanufacture including the step of introducing, subsequent to thehardening operation, the heat for the drawing into the article on aside-remote from the hardened surface.

Another object is the provision of a new and improved method of drawinga hardened surface on a curved or flat metallic member having adjacentsurfaces in the relatively unhardened state which comprises applyingheat, subsequent to the hardening operation, as by electricinductionheating to the unhardened surface and allowing the heat to flowby conduction to the hardened surface.

The" invention is applicable to any metallic article having a surfaceportion or. layer which must be heated throughout its thicknessuniformly and to a readily controlled amount.

The invention will be described as embodied in and applied to a cylinderliner which has an inner quench-hardened layer or surface, although itis equally applicable to other shapes of metallic articles eitherregular or irregular in shape or having continuous or discontinuoushardened surfaces.

Referring now to the drawings which are for the purposes of illustrationonly and not for limitation of the scope of the invention:

Figure 1 is'a side sectional view of a portion of i-arcylinderliner--having an inner hardened surface to bedrawn' to a lower hardnessand an electric induction-heating head adjacent the hardened surface tosupply the necessary heat;

-Figure 2 is a graph showing a group of typical curves of wall hardnessplotted against cylinder wall thickness and showing the hardnessvariations resulting from the method of heating shown in Figure 1;

Figure 3 is a view similar to Figure 1 but with the inductor forsupplying the drawing heat positioned adjacent a surface of the linerremote 3 Claims. (Cl. 148-215) from the hardened surface and embodyingthe present invention; and

Figure 4 is a view similar to Figure 2 but showing typical hardnesscurves obtainable by the present invention.

Referring now to Figure l, a portion of a cylinder liner I0 is shownformed of a material such as steel or the like having thecharacteristics which, in its initial unheat-treated state, is rela-'tively soft throughout but which can be hardened by heating above acritical temperature and interiorly of the liner and adjacent to theinnerv surface, thus inducing high frequency electric currents to flowin the surface II to raise its temperature above the criticalquench-hardening temperature. Subsequently, the surface is rapidly andforcefullyquenche'd by a quench head or the like not shown. v v j "CurveA of Figure 2 shows a typical hardness curve obtainable by using theabove, described electric induction heating and quench method. As shownby this curve, the initial hardness of,

the metal of the cylinder wall was 10 Rockwell C. The quench-hardeningoperation increased the hardness on the inner surface of the liner toRockwell C, which high hardness extendedfrom the inner surface of theliner outwardly for about a third of the thickness of the wall andthendropped rapidly in a very short wall, thickness to;

the initial hardness of 10 Rockwell C. j

Such heat-treating methods oftentimes 'produce surfaces harder than aredesiredor produce surfaces which have high internal stresses thereinwhich must be remcvedeven at the.

sacrifice of some of the hardness of the surface. It is known that asthe hardened surface or layer I I is reheated to sometemperature belowthe critical temperature, a softening of thehardened layer will resultdependent on the temperature and the length of time that thelayer isheld at that temperature together with a simultaneous,

very substantial relief of the internal stresses...

This operation is called a drawing or tempering operation. 1 I

To perform this drawing operation on cylin der liners for example, ithas been conventional a method of supplying the heat for drawingoftentimes produces an undesirable final hardness pattern in that theabsolute outer surface of the hardened layer draws to a greater degreethan the portions of the hardened layer more a remote from the outersurface.

As an illustration of this fact, assume for example it is desired todraw the. surface, of the.

hardened layer to 44 Rockwell C. 'Curve B of 4 vention comprisesintroducing the heat into areas of the metal where overheating has noill effects and allowing this heat to flow by conduction into thehardened area.

Thus, in the embodiment of the invention shown, the cylinder liner II]of Figure 1 with its internally hardened layer I I has the heat appliedexternally thereto; that is, on the side remote from the hardened layerI I and the heat is :allowed to flow into the hardened layer byconduction. This process is in contra-distinction to that shown inFigure 1 where the heat is generated in the hardened layer itself. Inthe embodirnent shown in, F ure 3, an induction-heating jjCOil I5 ispositioned exteriorly of the cylinder liner in and is connected to asuitable source of high-frequency electric energy not shown. High-Figure 2 is typical of the hardness pattern which j will result. Thesurface area as shown by the curve will be, of the required hardness.ever portions intermediate the surface of the hardened layerand theunhardenedfportion I2 will be drawn to a lesser degree and will have ahardness somewhat between the desired {24 R0019,

well C and the initial hardness.

Assumefurther that it is desired to obtain a maximum, hardness of 44Rockwell C through thehardened layerl I. Obviously, thetemperatureofthe. hardened layer must be increased or thev layer must'beheld at this temperature for. a longer period of time. Curve C of'Figu're 2 represents typical results. While the maximum hardnessv hasbeen reduc'ed to 44 Rockwell C, the hardness at the. surface of. thehardened layer .I I is substantially belowthat and is shown at 22Rockwell C.

Without limitation on the scope of the invention bdt rather. to aid inan explanation thereof, applicant advancesthe following theory forthisvariation in hardness pattern. As is known, high-frequency inducedcurrents of the metallic article-arefconcentrated almost entirely at andimmediately below the surface of the member adjacent theinduction-heating head. For pro ducing hardened layers of shallow depth,this is extremely desirable but for drawing purposes, applicant advancesthe theory that this concentration of currents at the surface causes thevariation in hardness pattern. cylinder-wall is to be heated through, itis obviousfroman examination of heat-flow theory that the source of theheat must be at some.

temperatureabove theportions of the wall to which the heat can flow byconduction. In the presentinstance, the source of the heat isinteriorlyj'of the .metal itself but still adjacent a surface oppolsitetheheating head. A temperature pattern somewhat as indicated by thecurve t1 is ,believedjto occur, the elevated portions of theicurvebeingthat where the currents themselves flow. It is believedthat thisaccounts for the increased draw adjacent the inner surfaces of i thecylinder liner.

The presentinvention contemplates a method of drawing 'metal articleshaving a hardened layer such as the cylinder of Figure 1 whereby. anevehtemperature and thus drawing of the. hardened layer II may beobtained throughout Generally speaking, 'the its entire thickness. 7invention comprises generating the drawing heat or intro'ducing thedrawing heat into the metal:- at a point remote from the hardened layeritself. and allowing the heat to flow thereinto by conuii a. Fplcillsn ss S aki ma How-.

As. the entire.

frequency heating currents still flow only adjacent the surface of theliner opposite from the induction-heating coil itself. No heatingcurrents in the embodiment shown in Figure 3 will flow within thehardened layer. Thus, the heat is generated only in the soft portion I2and flows to the hardened layer I I by thermal conduction, V Atemperature curve such as that indicated by #2 will generally existacross the thicknessof the liner wall. It will be obvious from thiscurye that the temperature in the hardened'layer itself will besubstantially uniform throughout its entire thickness, that the. highertemperatures generated in the wall are actually generated, in the layerI2, which is essentiallysoft'and will not be effected by heating to atemperaturebelow the critical. I

by heating externally. For example, ahigher rate of power can be appliedinitially resulting.

in the outer wall of the liner being atamo re; elevated temperature; forexample, such-as ;that,

shown by curve ts- The flow of heat-by conduction soon levels out thetemperature.-

It willbe appreciated that the induction-heap. ing coil I5 may be of anyknown type and may' be progressively moved along; the cylinder liner ormay be held stationary.

Curve D of Figure 4 shows a typical hardnesspattern'resulting from thedrawing operations following the teachings of this invention. .It willbe noted that this curve shows a substantially uniform hardness obtainedthrough the; hard,.

ened layer II after the drawing operation.

It will be obvious that the present invention is not limited to cylinderliners. It can beused on any other metallic articles having hardened; orother layers produced by any known means,

The hardened layersneed not be electrically .COIl-y ductive. It issufficient that the heating be gen; erated elsewhere than in thehardened surface.

itself. Radiant heat in the embodimentshown in Figure 3 could besubstituted for the inductionheating coil I5.

Other modifications will occur ;to others upon a reading andunderstanding of this specification. It is my intention-to cover allsuch modifi'-' cation insofar as they come within the'scope of theappended claims. Y Having thus described my invention, I claim: 1. Themethod of heat treating a metallic article of manufacture for thepurpose of drawing a previously hardened surface layer portionthereof,said article having a body portion and; a surface layer portion on eachside of said body portion, one of said surface layer portions beingpreviously hardened, which comprises subse'- quently applying heat tosaid other surface layer It is possible to obtain a more; rapid heating,

which comprises subsequently applying heat to said other surface layerportion to raise the temperature thereof above the temperature of saidother portions of said article. jto conduct said heat through said bodyportion and into said previously hardened surface layer portion to drawsaid last portion. 1-

3. The method of heat treating a metallic article of manufacture, saidarticle having a body portion and a surface layer portion on each sideof said body portion, which comprises heating one of said surface layerportions to quenchhardening temperature, quench-hardening said surfacelayer portion, subsequently applying heat to said other surface layerportion to raise the temperature thereof above the temperature of saidother portions of said article to conduct said heat through said bodyportion and into said quench-hardened surface layer portion to draw saidquench-hardened surface layer portion.

ANTON W. HERBENAR.

REFERENCES CITED The following references are of record in the file ofthis patent: v

UNITED STATES PATENTS N, b''r Name Date 2,295,272 Somer Sept. 8, 19422,303,467 Inskeep Dec. 1, 1942 FOREIGN PATENTS Number." Country Date 1485,733 Great Britain May 19, 1938

1. THE METHOD OF HEAT TREATING A METALLIC ARTICLE OF MANUFACTURE FOR THEPURPOSE OF DRAWING A PREVIOUSLY HARDENED SURFACE LAYER PORTION THEREOF,SAID ARTICLE HAVING A BODY PORTION AND A SURFACE LAYER PORTION ON EACHSIDE OF SAID BODY PORTION, ONE OF SAID SURFACE LAYER PORTIONS BEINGPREVIOUSLY HARDENED, WHICH COMPRISES SUBSEQUENTLY APPLYING HEAT TO SAIDOTHER SURFACE LAYER PORTION TO RAISE THE TEMPERATURE THEREOF ABOVE THETEMPERATURE OF SAID OTHER PORTIONS OF SAID ARTICLE TO CONDUCT SAID HEATTHROUGH SAID BODY PORTION AND INTO SAID PREVIOUSLY HARDENED SURFACELAYER PORTION TO DRAW SAID LAST PORTION.